1. Field of the Invention
The present invention relates to a portable electric heater, and more particularly to a improved flat panel heater having a flat panel heating element with a plurality of heating zones creating an efficient heating utilizing a planar air flow over the heating element.
2. Description of the Prior Art
Portable electric heaters are commonly used in many offices and households. Portable electric heaters in general are well known in the art and commonly used. Prior designs of heaters typically involve using a forced air system where a heating coil or other resistance type wire is used to supply heat after a current is passed through it. A fan is located adjacent the heating coil to blow air over the heated coil, thereby warming the air.
U.S. Pat. No. 5,655,055 to Goldstein et al. discloses a heater having a cylindrical housing with a fan blade positioned on the bottom of the housing below a heating element. Goldstein et al. discloses that the fan will blow air upward in a forced manner past the heating element through the housing and then through vents out of the housing. The air would become heated by passing over the heating element.
However, one disadvantage of heaters designed in this manner is that the heating element must become extremely hot in order to sufficiently heat the air moving past it, since the air is only passing over the heating element for a brief period of time. In addition, another disadvantage to this design is that the forced air from the fan may not flow evenly over the heating element, therefore the heating element is not cooled at an even rate creating an inefficient heater.
To address both problems, flat panel heaters have been created to provide a more even heat flow from the heating element itself. These flat panel heaters are typically shaped in large rectangular shapes and are heated so that the air immediately adjacent to the flat panel heater is heated. U.S. Pat. No. 6,134,386 to O""Donnell discloses a flat panel heater. The heater disclosed has a plurality of coils running beneath the surface of the flat panel heater which heats the top surface of the flat panel heater. The heating coils underneath the top surface heat the entire top of the flat panel heater thereby increasing the amount of air that is warmed immediately adjacent to the heater. One disadvantage of this design is that the flat panel heater only heats the air which is immediately adjacent to the flat panel heater itself, thus should the air be stagnant, very little volume of air is heated.
Therefore, in view of the prior art it would be desirable to have a heater which efficiently and evenly cools the heating element.
It would further be desirable to have a portable electric heater which creates an even flow of warm air being discharged from the unit.
It is an object of the present invention to provide a heater having an efficient heating element.
It is an object of the present invention to provide a flat panel heater having a heating element with a plurality of heating zones.
It is another object of the present invention to provide a heater having a planar and homogeneous air flow to provide even cooling of the heating element.
According to the heater of the present invention, the heater includes a housing having sidewalls defining an interior space that holds a heating element. The heating element is preferably in the form of a flat panel having a lower portion and an upper portion, wherein the heating element has differing power densities from the lower portion to the upper portion. The heater also includes a heat shield positioned in substantially parallel relation to the heating element to create a duct for directing air flow therethrough. To move the air over the heating element, the heater is provided with an air displacement device positioned adjacent to the heating element providing a planar flow of air through the duct. The heater may be controlled by a control circuit having a circuit board, which controls the power supplied to the heating element and the air displacement device.
In the preferred embodiment of the present invention, the air displacement device is a fan having a fan housing holding a motor connected by a shaft to at least one fan blade rotatably mounted to the motor. The fan housing may have an outlet directed toward the duct and an inlet for drawing air into the fan. The fan preferably uses a first squirrel cage fan blade positioned in linear alignment with a second squirrel cage fan blade so that a single motor may be used to rotate both fan blades. The squirrel cage fan blade is positioned so that air exiting the fan is directed into the duct. Some of the air may flow over the front face of the heating element opposite the duct.
The heating element is preferably made of a heat conductive material such as steel and is substantially flat and has a rectangular shape. The heating element is preferably positioned in a substantially vertical orientation within the heater housing and the axis of rotation of the fan blade is substantially perpendicular to the longitudinal axis of the heating element. The heating element may use an electrical resistance element which is attached to the heating element to create the power density. The electrical resistance element is preferably a continuous resistance wire made of an electrically conductive material, such as copper, that releases heat when a current is passed through it. The continuous resistance wire may be positioned on the heating element in an xe2x80x9cSxe2x80x9d curve configuration so that the element is spaced closer to itself on the lower portion of said heating element and is spaced a distance further apart on the upper portion of the heating element, thereby creating differing heating zones in the heating element. Preferably there is a first resistance wire and a second resistance wire positioned in parallel relationship to each other and power to the heating element is controlled by the electronic control circuit.
An advantage of the present invention is that the heating element has differing different heating zones thereby increasing the output efficiency of the heater. The bottom of the heating element is heated at a higher rate so that the high speed air at ambient temperature drawn in by the fan and directed over the heating element will be heated quickly by the higher power heating element portion at the lower end of the heating element. After passing over the lower portion, the now slower moving air passes over the upper portion and will stay in contact with the heating element a longer amount of time than it did at the lower portion. Therefore, the upper portion does not have to be as hot as the lower portion to sufficiently heat the air. The air will then pass over the upper portion and flow out of the duct into the space to be heated.
A further advantage of the present invention is that the air which exits the fan is directed in a substantially planar manner over the heating element so that its surface is cooled at a substantially even rate. The combination of the duct and the varying power density of the heating element create an environment where the heating element is cooled in a homogenous and even rate.
In order to provide a safer heater, the preferred embodiment of the present invention includes a control circuit having a circuit board controlling the current supplied to the heating element and the motor. The control circuit may include a current limiting sensor and a thermister to both prevent the heating element from over-heating and limit the amount of heat produced by the heater. The circuit board also includes a power light to alert the user when the heater is activated. In addition, a tip over switch may be mounted to heater, so that if the heater were to tip over, it would automatically shut off the fan and the heating element.
A preferred form of the portable electric heater, as well as other embodiments, objects, features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments thereof, which will be read in conjunction with the accompanying drawings.